The present invention relates generally to miniature motors and bearing devices thereof, more particularly, to bearing devices suitable for motors employed in office automation (OA) apparatuses such as personal computers, work stations and laser-beam printers, or audio-video (AV) apparatuses such as Digital Versatile Disc (DVD) apparatuses and Video Cassette Recorders (VCR).
OA apparatuses and AV apparatuses use plural motors per apparatus as their driving sources. Those motors mainly use oil impregnated sintered bearings because of inexpensive cost and easy handling.
Those motors employed in OA apparatuses and AV apparatuses have frequently spun at higher speeds than conventional motors due to recent speeding up and sophistication of the apparatuses. For instance, a spindle motor for driving a disc of a CD-ROM device mounted in a personal computer is required to spin as fast as 10,000 rpm although a conventional motor spins at several hundred rpm.
The speeding up and sophistication of the foregoing apparatuses remarkably increase information volume processed in electronic circuits of the apparatuses, and the electronic circuits thus generate greater heat amount. A blower, using a fan driven by a motor, for cooling the heat amount draws attention from the market, and a fan motor is also required to spin faster.
In general, those OA and AV apparatuses are used on a maintenance-free basis, and the service life of those apparatuses often depends on the life of bearings of the motors used in the apparatuses. A longer life has been demanded of the bearings in order to extend the service life of the apparatuses.
A conventional bearing disclosed in Japanese Patent Gazette No. 2903664 has been well known. FIG. 12 shows a structure of the conventional bearing device of a motor. In FIG. 12, shaft 104 fixed to rotor 108 is rotatably supported with oil impregnated sintered bearing 103. A first end of bearing boss 102 which firmly holds bearing 103 is sealed with cap 109 to prevent lubricant 115 from leaking. At a second end (open end) of boss 102, oil shield washer 105 is provided, grooves are formed on an outer wall of bearing 103, and grooves are formed on bearing boss 102. This structure prevents lubricant 115 from leaking out to outside of the bearing device. Stopper 106 is rigidly mounted to shaft 104 to prevent shaft 104 from coming off. Between stopper 106 and a lower end of bearing 103, thrust plate 107 is prepared.
In the foregoing structure, however, the motor is forced to increase its rpm due to speeding up and sophistication of the apparatus, so that the temperature of the bearing rises due to the lubricant""s viscous heat as well as an increase in the load in the radial direction due to an imbalance of the rotor. As a result, the foregoing structure cannot extend the motor""s life or even maintain the present rated life.
A service life of a bearing is determined by the factors such as degradation or consumption of lubricant impregnated in the oil impregnated sintered bearing, or wear of a sliding face of the bearing. In the foregoing conventional bearing device, the first end of the bearing is completely sealed with the cap, and lubricant leaks out from the oil impregnated sintered bearing due to temperature rise or vibration during the operation and pools in the cap. The lubricant pooled cannot return into the bearing, so that the amount of the lubricant in the bearing eventually decreases. The sliding face of the shaft thus cannot be protected with sufficient lubricant. This is the same phenomenon as occurs when the lubricant is consumed. As a result, the service life of the bearing device is shortened.
The present invention addresses the problem discussed above, and aims to provide a bearing device that can supply lubricant within the device effectively to the sliding face of a shaft, thereby extending a service life of the bearing device.
The bearing device of the present invention comprises the following elements:
an oil impregnated sintered bearing rotatably supporting a shaft rigidly mounted to a rotor;
a bearing boss firmly holding the bearing with an inner wall of the bearing boss; and
a cap for sealing an end of the bearing boss.
A plurality of grooves are formed on the inner wall of the cap for retaining the lubricant leaking out from the bearing and for returning the lubricant to the bearing. This structure allows stable supply of lubricant to the sliding face of the shaft, so that the service life of the bearing is extended.